This made me lol
A life lesson here.
I got it correct but I think "他很帅，但不是个好人" is more natural here...
Would the sentence still work without the 一个?
Yes I used it without the 一个 and it was accepted
"可是" should be accepted in place of "但是".
You could also use 壞蛋 literally means (bad egg)
But that is a bit informal, and mostly only children use it. Kind of like the word "tummy" - most adults don't really use it much.
if you use spaces in your Chinese sentence, Duo will reject your answer.
I wrote 他很帅，可是不是好人 and because I heard it in the Chinese drama, and got marked right, but what is the difference between 可是 and 但是?
There's no big difference. "但是" is ever so slightly more formal.
no need for “雖然” here?